Fuel cells have been identified as a relatively clean and efficient source of electrical power. Alkaline fuel cells are of particular interest because they operate at relatively low temperatures, are efficient and rugged. Acid fuel cells and fuel cells employing other aqueous electrolytes are also of interest. Such fuel cells typically comprise an electrolyte chamber separated from a fuel gas chamber (containing a fuel gas, typically hydrogen) and a further fuel gas chamber (containing an oxidant gas, usually air). The electrolyte chamber is separated from the gas chambers using electrodes. Typical electrodes for alkaline fuel cells comprise a conductive metal grid or mesh backbone, typically nickel, that provides mechanical strength to the electrode. Onto the metal mesh or grid is deposited a catalyst as a slurry or dispersion of particulate poly tetra-fluoroethylene (PTFE), activated carbon and a catalyst metal, typically platinum. Such electrodes are expensive, electrically lossy, thick, heavy and suffer from irregular distribution of catalyst. Furthermore, the nickel mesh is prone to breakage and causes local irregularities and unwanted variations in electric field due to resistance at the contact points between the wires of the mesh.
A problem with many known fuel cell assemblies is that liquids (typically water), that are a product of the chemical reactions occurring at the electrodes, are trapped in the gas chambers, and the liquid has to be removed from the gas chambers by a water management system including pumps, dehumidifiers, drainage channels or the like adding to the complexity of fuel cells. The loss of liquid reaction products from the electrolyte chamber also means that the electrolyte needs to be constantly topped up either with recycled lost liquid or additional fresh liquids. Furthermore, the presence of the liquid reaction products (especially water) in the fuel cells reduces the capability of fuel cells to operate at low temperatures approaching the freezing point of the liquids.
Some of the problems had been previously addressed by Shell (UK patents 874,283 and 951,807) who deposited a conductive metal layer onto a relatively non-conductive, porous, rigid substrate made of Porvic® a sintered microporous polyvinylchloride (PVC) material. The electrodes of Shell were still relatively thick and the process used to manufacture the Porvic® substrate used chemicals that require careful handling and disposal. Furthermore, the Porvic® plastic material is hydrophobic (requiring alcohols such as n-propanol or n-butanol in order to wet the substrate) and so aqueous electrolytes are not readily absorbed into the pores of the electrode substrate.